Generally, a modern passenger vehicle has many electrically controlled actuators with electric motors. For example, actuators are used in safety mirrors, seats, and vehicle air conditioning systems where they control flaps or barriers used to control or redirect air flow within the vehicle for allowing more or less air to pass over a heat exchanger coil or directing air to certain parts of the vehicle such as windscreen vents or feet vents. The electric motors moving these flaps are generally controlled from a centralized control panel or, when fitted, from a remote control panel. Automate control of the air conditioning system based on sensor feedbacks, etc is also allowed.
Previously, these motors were generally PMDC (Permanent magnet direct current) brush motors. This type of motors is easy to control manually, has acceptable life and is relatively cheap. However, they are noisy either audibly, electrically or both. Noise is becoming a problem in the modern passenger vehicle. Audible noise generated by the motors has become very noticeable as passenger compartments are being effectively isolated from road and engine noise. Electrical noise is also undesirable as the modern vehicle has multiple computer systems and electronic devices susceptible to electrical noise. For automated systems controlled by a computer, such as mirror, seat, and temperature controls with memory, the motors are connected to the computer via a computer bus such as a LIN Bus or CAN Bus. Electronically controlled motors are more suited to this kind of system. One drawback to using electronically controlled motors is the cost of the electronics may be more than the cost of the motor being controlled. In an air conditioning system, the temperature changes occur slowly and thus most of the time the motors are idle. The seat and mirror memory systems may be operated only when there is a change of driver.
A typical computer controlled system is shown in FIG. 1. An on board computer system 10, which maybe a single computer or a number of computers linked together, is referred to as a CPU. A plurality of motors, M1, M2, . . . Mn, are connected to the CPU 10 via a LIN bus system 12. This requires each motor 31 to be fully independent, having its own LIN bus driver 23, MCU 21, feedback sensor 33, power switch 24 and identifier 32. This is expensive in terms of electronic hardware which is used only occasionally.